Portable keyboard



FIG. 1 is a front right perspective view of a portable keyboard showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is a closed view thereof. 

The ornamental design for a portable keyboard, as shown. 